The present invention relates generally to a printer device employing a scanning printing head, but particularly, although not exclusively, to a method of increasing the throughput of an inkjet printer device and the corresponding apparatus.
Inkjet printer devices generally incorporate one or more inkjet cartridges, often called xe2x80x9cpensxe2x80x9d, which shoot drops of ink onto a page or sheet of print media. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. The pens are usually mounted on a carriage, which is arranged to scan across a scan axis relative to a sheet of print media as the pens print a series of individual drops of ink on the print media forming a band or xe2x80x9cswathxe2x80x9d of an image, such as a picture, chart or text.
Inkjet printers are generally arranged to print in a variety of print modes that offer differing trade-offs between print quality and throughput. In high throughput modes, the print media may be advanced relative to the carriage by a distance equal to the height of a swath once a given swath is printed. In this manner, a further swath may then be printed adjacent to the earlier swath. By a repetition of this process, a complete printed page may be produced in an incremental manner.
Over recent years, the importance placed on the throughput of ink jet printers has risen dramatically. Throughput is generally measured as the number of pages of a given size, or the area of print media that a printer may ink in a given time. Consequently, manufacturers of inkjet devices have embarked on a process of continually improving their inkjet printers to give improved throughput in order to secure a competitive edge in the marketplace.
Throughput is directly related to the speed at which each swath may be printed. Therefore, in order to enable higher throughputs, inkjet devices have been developed to print at higher carriage speeds, thus allowing more swaths to be printed in a given time. However, as the carriage speed increases above a certain point, the print quality tends to deteriorate. In many cases it is preferable to print images of higher quality at a lower throughput than lower quality images at a higher throughput. Consequently, inkjet printers are being continually redeveloped to use printheads having increasingly large swath heights. By using printheads with larger swath heights, fewer swaths are needed to print a given print job. Thus, throughput may be increased.
However, even with the advent of printheads with a swath height of approximately an inch, and the prospect of printheads with significantly greater swath heights being developed in the future, the demand for yet further increases in throughput remains. This is particularly true as inkjet technology is now being used or considered for use in fields traditionally dominated by other technologies.
It would therefore be desirable to provide an improved inkjet device and a method of operating an inkjet printer that addresses the problems of the prior art.
According to the present invention there is provided an inkjet device comprising a printhead and a media advance mechanism, the printhead being arranged to print swaths aligned in a first direction, each swath having a width in a second direction substantially perpendicular to said first direction, said media advance mechanism being arranged to feed a print medium relative to said print head to position said swaths in the second direction on the print medium, the device being arranged to print an image having a length in said second direction and comprising a plurality of swaths spaced apart in said second direction, said device being further arranged to reduce the width of one or more of said plurality of swaths in dependence upon the image length in order to reduce the total time to feed said print medium.
The inventors of the present invention realised that, paradoxically, by reducing the swath height used to print an image, the throughput of the printer may be increased.
When printing an image with an inkjet printer, the exact distance by which the print media must be advanced must, in general, be controlled very accurately in order to ensure good registration between consecutive swaths. This is carried out while the printer is not printing; i.e. in between swaths. Experience has shown that to advance the print media with sufficient precision generally requires a period of time that is significantly longer than the time required for the printer carriage to xe2x80x9covertravelxe2x80x9d beyond the edge of the print media, having completed one swath, to decelerate and then re-accelerate in the reverse direction prior to printing a further swath. Thus, the print media advance time has a direct impact on the time taken to print an image.
It frequently arises that the length of the image in the direction perpendicular to the scan axis (image length) is a non-integer multiple of the swath height of the printheads. This means that only a fraction of the swath height of the printheads remains to be printed in the last pass of the printheads over the print medium. The inventors of the present invention realised that in such cases, fixed media advances of the prior art gives rise to a non-optimal total time required to advance the print media in printing an image.
In such cases, an image or print job, is, according to one aspect of the present invention, printed using swaths of reduced height, by using only selected printhead nozzles. Preferably, the printer uses a reduced swath height which is equal to the largest fraction of the maximum swath height of said printhead for which the said image length is an integer multiple. This in turn proportionally reduces the distance of media advances between swaths. By reducing the swath height to the largest fraction of the printhead swath height of which the image length is an integer multiple, the total media feed time may be optimised, without increasing the number of swaths required to print the image. In this manner, the time required to print the image may be reduced and the throughput of the printer correspondingly increased.
The degree to which the throughput may be increased in this manner is dependent upon several factors. These include: the minimum number of swaths required to print the image; and, the proportion of the full printhead swath height that would normally be printed in the last pass using constant media advances, when printing a given image. However, in general, the invention is best suited to printers having a large swath height, and furthermore to printers having a swath height that large in relation to the length of the image. The throughput advantages of the present invention are particularly beneficial in devices required to print many images, or copies of an image, rapidly. For example, wherein the inkjet device is being used in the role of the printing engine of a photocopier.
The present invention also extends to the method corresponding to the method. Furthermore, the present invention also extends to a computer program, arranged to implement the method of the present invention.